"You cannot believe how hard it is to motivate people in the field who know that all they are doing is going through busy work motions because they themselves know there are no weapons there.

"I faced that over a year ago with a team that essentially knew that we were right when we said they were no weapons."

He said the ISG's document search would now focus on the continued insurgency in Iraq and the money flow issue surrounding the oil-for-food programme.

Former head of UN weapons inspections Hans Blix also said there was no surprise in the announcement.

"We have believed that there weren't any weapons since around May or June 2003. First came David Kay in September 2003 [who said] that he hadn't found any weapons and that was a big sensation - but he thought that there were programmes still," he told the BBC.

"But then came Duelfer last November [who] said that he hadn't seen any programmes, but maybe Saddam would have intended to restart the programme, and there is no evidence of that.

Mr Blix said he assumed it would be natural for the United States to now report their finding to the UN Security Council "because the US took the inspections out of the hands of the UN to undertake it themselves".